Mechanical Heat Meters

A mechanical heat meter measures the flow rate with an impeller turned by the water flow and the supply–return temperature difference with a pair of temperature sensors, and calculates the heat consumed from these two values. The Minol Zenner C5 ISF DN20 in this category is a threaded apartment meter with a single-jet flow sensor and can be ordered with wired M-Bus or wireless wM-Bus communication. Its body length and connection thread are the same as those of ultrasonic models of the same size. It suits like-for-like replacement of an existing mechanical meter and projects where budget is the priority. For models with no moving parts, see the ultrasonic heat meter category.

Mechanical vs. Ultrasonic Heat Meters

The values below are taken from the manufacturer’s data sheets for two compact meters of the Minol ZENNER group’s C5 family: ZENNER zelsius C5-ISF (mechanical) and C5-IUF (ultrasonic).

In short, the ultrasonic meter measures low flow rates over a wider range and has no wearing parts, while the mechanical meter is a more economical and familiar solution from the same brand.

When to Choose a Mechanical Heat Meter

• When the apartment already has a mechanical meter and you want a quick swap with the same size, the same body length (130 mm for DN20) and the same connection.
• When the installation is for heating only: the C5 ISF model on our site is listed for heating applications.
• In closed circuits with good water quality where the strainers are cleaned regularly.
• In projects where budget is the priority but remote reading is also required: hot and cold water meters can be connected to the three pulse inputs of the C5 ISF so that all of them are read over the same line.

If cooling is to be metered as well, or if the system runs at very low flow rates for long periods, an ultrasonic model is the better choice.

Water Quality, Wear and Maintenance

A mechanical flow sensor has an impeller that turns in the water. Sand, welding slag, sediment and magnetite in the system can hinder the free rotation of the impeller and affect the measurement. For this reason, a strainer should be installed upstream of the meter and cleaned regularly, and isolation valves should be fitted before and after the meter. In new installations, flushing the pipes before commissioning extends the life of the impeller. The reducing adapters needed for the sensor connection are in the heat meter spare parts category.

Re-verification

Where national regulations require periodic re-verification of heat meters, the requirement applies to mechanical models just as it does to ultrasonic ones; intervals and procedures differ from country to country. Check your local regulations for periodic re-verification requirements. A meter that fails re-verification is repaired and recalibrated or replaced; when replacing it, you can also switch to a DN20 ultrasonic heat meter with the same size and body length. For more information, see our Heat Meter Re-verification and Calibration page.

For the working principle, types and size selection of heat meters, see our guide What Is a Heat Meter?

Frequently Asked Questions

What is the difference between a mechanical and an ultrasonic heat meter?

A mechanical heat meter measures the flow rate with an impeller turned by the water; an ultrasonic heat meter measures it from the transit time of sound waves. The ultrasonic model has no moving parts and, according to manufacturer data, a better accuracy class (class 3 for mechanical, class 2 for ultrasonic).

Can a mechanical heat meter be read remotely?

Yes. The Minol Zenner C5 ISF can be ordered with wired M-Bus or wireless wM-Bus communication, so it can be read without entering the apartment.

Can an ultrasonic meter replace a mechanical meter?

If the size, body length and connection thread are the same, usually no change to the installation is needed. The technical tables of the DN20 mechanical and ultrasonic models on our site give a body length of 130 mm and a 1” connection thread.

How often must a mechanical heat meter be re-verified?

Re-verification intervals for heat meters, mechanical or ultrasonic, are set by national regulations and vary from country to country. Check your local regulations for periodic re-verification requirements.